This strikes me as not dissimilar to religious people who are terrified of atheists because, without God, they must have no reason not to become mass murderers.

This strikes me as not dissimilar to religious people who are terrified of atheists because, without God, they must have no reason not to become mass murderers. There are many people with kids who have revealed the value they place on the sustainability of the environment, democratic society, or the economy through the lifetime of their children, let alone their children's children, to be zero. Why would you assume that the childless are any more selfish, as a group? Why can one not care about the continuance and betterment of humanity without one's own direct descendents being involved?